#### 12th Standard English Medium Physics Reduced syllabus Annual Exam Model Question Paper with Answer key - 2021

12th Standard

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Physics

Time : 02:45:00 Hrs
Total Marks : 70

Part I

Choose the most suitable answer from the given four alternatives and write the option code with the corresponding answer.

15 x 1 = 15
1. Two identical point charges of magnitude –q are fixed as shown in the figure below. A third charge +q is placed midway between the two charges at the point P. Suppose this charge +q is displaced a small distance from the point P in the directions indicated by the arrows, in which direction(s) will +q be stable with respect to the displacement?

(a)

A1 and A2

(b)

B1 and B2

(c)

both directions

(d)

No stable

2. An electric field $\vec { E } =10x\hat { i }$ exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

(a)

10 V

(b)

-20 V

(c)

+20 V

(d)

-10 V

3. The relative permittivity of water is _______.

(a)

ε= 70

(b)

ε= 75

(c)

ε= 80

(d)

ε= 85

4. A toaster operating at 240 V has a resistance of 120 Ω. The power is ___________

(a)

400 W

(b)

2 W

(c)

480 W

(d)

240 W

5. In a large building, there are 15 bulbs of 40W, 5 bulbs of 100W, 5 fans of 80W and 1 heater of 1kW are connected. The voltage of electric mains is 220V. The minimum capacity of the main fuse of the building will be ______________

(a)

14 A

(b)

8 A

(c)

10 A

(d)

12 A

6. The temperature coefficient of resistance of a wire is 0.00125 per °C. At 300 K, its resistance is 1 Ω. The resistance of the wire will be 2 Ω at ______________

(a)

1154 K

(b)

1100 K

(c)

1400 K

(d)

1127 K

7. Two identical coils, each with N turns and radius R are placed coaxially at a distance R as shown in the figure. If I is the current passing through the loops in the same direction, then the magnetic field at a point P at a distance of R/2 from the centre of each coil is ____________

(a)

$\frac { 8N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

(b)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }^{ \frac { 3 }{ 2 } }R }$

(c)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }R }$

(d)

$\frac { 4N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

8. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.

The potential difference developed across the ring when its speed v, is _____________

(a)

Zero

(b)

$\frac { { Bv\pi { r }^{ 2 } } }{ 2 }$ and P is at higher potential

(c)

πrBv and R is at higher potential

(d)

2rBv and R is at higher potential

9. Which of the following is an electromagnetic wave?

(a)

α - rays

(b)

β - rays

(c)

$\gamma$ - rays

(d)

all of them

10. An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is _________

(a)

8 cm

(b)

10 cm

(c)

12 cm

(d)

16 cm

11. The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is _____________

(a)

4125 $\mathring { A }$

(b)

3750$\mathring { A }$

(c)

6000$\mathring { A }$

(d)

2062.5$\mathring { A }$

12. The mass of a 37Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of 37Li nucleus is nearly _________

(a)

46 MeV

(b)

5.6 MeV

(c)

3.9 MeV

(d)

23 MeV

13. In a Young’s double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to ______________

(a)

2D

(b)

$\frac{D}{2}$

(c)

$\sqrt{2}$D

(d)

$\frac{D}{\sqrt2}$

14. If the input to the NOT gate is A = 1011, its output is ___________

(a)

0100

(b)

1000

(c)

1100

(d)

0011

15. The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called _________________.

(a)

Amplitude modulation

(b)

Frequency modulation

(c)

Phase modulation

(d)

Pulse width modulation

1. Part II

Answer any 6 questions. Question no. 16 is compulsory.

6 x 2 = 12
16. When does a dielectric said to be polarized?

17. An electric dipole is held in a uniform electric field.
(i) Straight the net force acting on it is zero.
(ii) The dipole is alignment parallel to the field. find the work done in rotating it through the angle of 180o.

18. Two isolated metal spheres A & B have radii R & 2R respectively and same charge q. Find which of the two spheres have greater energy density just outside the surface of the sphere.

19. A particle of mass m and charge (-q) enters the region between the two charged plates initrally moving along X-axis with speed Vx as shown in figure. The length of plate is L and an uniform electric field E is maintained between the plates. S.T. vertical deflection of the particle at the far edge of the plate is $\frac { q{ EL }^{ 2 } }{ 2m{ V }_{ x }^{ 2 } }$.

20. Why are household appliances connected in parallel?

21. Define resistance.

1. Part III

Answer any 6 questions. Question no.27 is compulsory.

6 x 3 = 18
22. Identify the following Electromagnetic radiations
(a) 109 Hz
(b) 1011 Hz.Give one application of each.

23. Derive an expression for De Broglie wave length.

24. The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs. Collector plate potential for three different intensities I1, I2, and I3having frequencies v1' v2 and v3 respective incident on a photosensitive surface.
The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs. Collector plate potential for three different intensities I1, I2, and I3 having frequencies v1,v2, and v3 respective incident on a photosensitive surface.

25. What is the diameter of H2 atom?

26. Write the drawbacks of Nicol prism.

27. What is electronics?

1. Part IV

5 x 5 = 25
1. Monochromatic light of frequency 6 x 1014 Hz is produced by a laser. The power emitted is 2.0 x 10-3 W. How many photons per second on an average are emitted by the source?

2. The two lines A and B in figure show the plot of de Broglie wavelength λ as a function of $\frac{1}{\sqrt V}$ for two particles having the same charge. V is the accelerating potential. Which of the two represents the particle of heavier mass?

1. When an electron in hydrogen atom jumps from the third excited state to the ground state how would the de Broglie wavelength associated with the electron change? Justify your answer.

2. An electron and a proton, each have de Broglie wavelength of 1.00 nm.
(a) Find the ratio of their momenta.
(b) Compare the kinetic energy of the proton with that of the electron.

1. For photo electronic effect in sodium, the figure shows the plot of cut-off voltage versus frequency of incident radiation. Calculate
(i) threshold frequency
(ii) work function for sodium.

2. Two singly ionized isotopes of uranium $_{ 92 }^{ 235 }{ Uand_{ 92 }^{ 238 }{ U } }$ (isotopes have same atomic number but different mass number) are sent with velocity 1.00 x 105 m s–1 into a magnetic field of strength 0.500 T normally. Compute the distance between the two isotopes after they complete a semi-circle. Also, compute the time taken by each isotope to complete one semi-circular path. (Given: masses of the isotopes: m235 = 3.90 x 10–25 kg and m238 = 3.95 x 10–25 kg)

1. What is the magnetic field at the centre of the loop shown in figure?

2. A bar magnet is placed in a uniform magnetic field whose strength is 0.8 T. If the bar magnet is oriented at an angle 30o with the external field experiences a torque of 0.2 Nm. Calculate
(i) the magnetic moment of the magnet
(ii) the work done by the magnetic field in moving it from most stable configuration to the most unstable configuration and also compute the work done by the applied magnetic field in this case.

1. Suppose a cyclotron is operated to accelerate protons with a magnetic field of strength 1 T. Calculate the frequency in which the electric field between two Dees could be reversed.

2. An electron in a hydrogen atom is moving with a speed of 2.3 x 106 ms-1 in an orbit of radius 0.53 Å. Calculate the magnetic moment of the revoling electron.